Happily, the director, Mark Waters, and the screenwriters, Heather Hatch and Leslie Dixon, are effortlessly attuned both to the brash bounce of current pop culture and to the wise, impish intergenerational comedy that has made the book a classic (and also inspired a 1976 movie that helped to make Jodie Foster a star). Loud but never coarse, candid without being prurient, ''Freaky Friday,'' which opens nationwide today, is a quick-witted, perfectly modulated family farce with a pair of beautifully matched performances from Ms. Lohan and especially Ms. Curtis, who does some of her best work ever.

Or make that four performances, since the story demands that the two actresses play not only their own characters but each other as well. Anna and Tess are locked in such a spectacular misunderstanding that only supernatural intervention can save them.

In her mother's eyes, Anna is loutish and irresponsible; to her daughter, Tess is an uptight control freak. Their reciprocal and chronic failure of sympathy catches the attention of the owner of a Chinese restaurant, who, over the protests of her own daughter, slips Tess and Anna a pair of magic fortune cookies. The next morning (the Friday in question, with a big test, a big audition and Tess's rehearsal dinner on the schedule) they wake up in each other's bodies.

I must confess to a special fondness for comedies in which the rules of time, space and logic are suspended so that misguided but essentially decent people can straighten themselves out. At bottom, these movies -- which include ''Groundhog Day,'' the many incarnations of ''Heaven Can Wait'' and ''All of Me'' -- are comic fantasies of moral improvement, and ''Freaky Friday'' belongs in their company. The measure of its integrity is that it moves smoothly, convincingly and with minimal self-consciousness from farce to earnest sentiment, earning your tears at the climactic mother-daughter rapprochement because it has treated you so generously to laughter on the way.

Both tears and laughter arise from the writers' canny and unforced understanding of what makes the characters tick. Anna and Tess are recognizable types but also solid, peculiar individuals, something that becomes clear only after their identity swap. Ms. Lohan's natural sullenness turns into primness; her back stiffens and her lips purse as she registers the anxious disapproval of a middle-aged woman for the chaotic youthscape into which she is plunged. Only when Tess is in Anna's body do we see the wistfulness and uncertainty beside her faÃ§ade of brisk confidence.

Similarly, it is only when Anna is thrown into her mother's unretouched middle-aged person that her fearless, reckless ardor for living comes into full view. Ms. Curtis's performance is a marvel. She does all the necessary slouching, grimacing and gesticulating of course, but there is a verve and conviction here that is downright breathtaking, especially in her scenes with Chad Michael Murray, whose character, a dreamy blond named Jake, is the object of Anna's clear-sighted but nonetheless intoxicating crush (and also the movie's chance to put a sweet new wrinkle into the older-women-with-younger-men theme).

As Jake and Anna -- who he thinks is her mom -- babble about their favorite and least favorite bands, you feel the rush of shared enthusiasm, the giddy sense of possibility and connection that accompanies first love.

Since her character wears no historical costumes and suffers from no debilitating ailment, it is likely that Ms. Curtis will be overlooked when Oscar season rolls around. This is a shame, since it is unlikely that any other actress this year will match the loose, energetic wit she brings to this delightful movie.

''Freaky Friday'' is rated PG. It has some very mildly suggestive moments and some equally mild naughty language.

FREAKY FRIDAY

Directed by Mark Waters; written by Heather Hach and Leslie Dixon, based on the book by Mary Rodgers; director of photography, Oliver Wood; edited by Bruce Green; music by Rolfe Kent; production designer, Cary White; produced by Andrew Gunn; released by Walt Disney Pictures. Running time: 93 minutes. This film is rated PG.